1. Field of the Invention
The present invention relates to a process for preparing cyclic siloxane, particularly from alkylhalosilanes or alkylalkoxysilanes.
2. Description of the Prior Art
Cyclic siloxanes are generally produced by hydrolyzing alkyldichlorosilanes which results in a mixture of cyclic siloxanes and linear polysiloxanes of various molecular weight. The preparation of cyclic methylsiloxanes utilizing methyldichlorosilane in a solvent system based on diethylether and crushed ice is disclosed by Sauer et al., J. Am. Chem. Soc., vol. 68, 962 (1946). The yield of the process is reported to be 56.7% with the remaining 43.3% being linear polysiloxane. In Curry U.S. Pat. No. 3,484,468 to Curry, a process for producing cyclic methylpolysiloxanes by hydrolysis of dichloromethylsilane in a solvent mixture of a tertiary alcohol and benzene is disclosed. The best yield of the process is reported to be 66% cyclosiloxanes and 34% linear polysiloxanes. In U.S. Pat. No. 3,763,212 to McEntee et al., a process for preparing cyclic sympolyalkylpolyalkenylpolysiloxane in a mixture of water and a water soluble aliphatic alcohol or aliphatic ketone is disclosed. The reference teaches that the ketone and alcohol must be completely soluble in water.
Cracking linear polysiloxanes at an elevated temperature in the presence of a catalyst is an alternative process for the production of cyclic siloxanes. However, the cracking process has not been widely utilized since the process must proceed from an intermediate polysiloxane and is energy intensive. Illustrative processes are disclosed in Miller et al. U.S. Pat. No. 3,714,213 to Miller eta l. and 4,895,967to Crivello et al.
This invention provides an improved process for producing cyclic siloxanes in high yield and with low energy consumption.